(1) Suppose your office has a safe. Your on-staff accountant has the combination and he supervises all access to the safe. But imagine the difficulties if the accountant fell seriously ill, or if access to the safe was needed on a holiday or weekend when the accountant couldn't be reached. Instead of giving the combination to several people as a backup--and thereby losing accountability--you can divide the combination between 4 people in which any 2 can reconstruct the key.
(2) You and your two fellow executives are flying into country X for important business meetings. The border control at country X is known to sometimes snoop on visitors laptops and smartphones, and even copying data. You and the two other travelers can split up your confidential documents such that all 3 of you must be present at the meeting to extract the confidential information. If one of you is searched at the border crossing, you can truthfully say that you don't know any password or passphrase to documents in your possession; only the assembly of 3 people can bring out the originals.
(3) Your company's long-term computer backups--made on network attached storage or to the cloud--are automatically encrypted. The decryption key can be shared between the system administrators and executives such that any 2 sysadmins or any 3 executives can recover the decryption key.
Indeed the distribution of the ciphertext when using Airdrop relies on the authentication made by Airdrop (I think that's why Airdrop requires iCloud to be enabled, but note I'm not sure of that). However the encryption of the ciphertext and the keys used are independant of Airdrop. In the worst case a wrong receiver would be selected, he would have the ciphertext but wouldn't be able to decrypt it.
edit: I think I've wrongly interpreted your question. Are you asking if Core Secret doesn't simply reimplement what Airdrop provides? If this is your question, the answer is no, the goal of Core Secret is to divide a secret between peers, each peer having a portion of the secret.
Tangently related question - is it possible to use Bluetooth API to send pictures between devices? I wonder if the bandwidth is too low, or if there any hoops for the user to jump through? Thanks
BLE provides different ways of making requests, it seems the mode with the highest throughputs is when the central (client) subscribes to notifications for a service on a peripheral (server) and the peripheral writes data to the central with or without responses.
Note that it certainly was tested on iOS 6 and iOS 7 has since improved its BLE stack implementation, for instance back then MTU was fixed to 22 bytes while it is now negociated and usually is around 112 bytes between 2 iOS 7 devices (iPhone 5).
What is this idea good for?
Who would use it?
Why is it needed?
Some actual uses cases are needed.
Allow me to start you off:
(1) Suppose your office has a safe. Your on-staff accountant has the combination and he supervises all access to the safe. But imagine the difficulties if the accountant fell seriously ill, or if access to the safe was needed on a holiday or weekend when the accountant couldn't be reached. Instead of giving the combination to several people as a backup--and thereby losing accountability--you can divide the combination between 4 people in which any 2 can reconstruct the key.
(2) You and your two fellow executives are flying into country X for important business meetings. The border control at country X is known to sometimes snoop on visitors laptops and smartphones, and even copying data. You and the two other travelers can split up your confidential documents such that all 3 of you must be present at the meeting to extract the confidential information. If one of you is searched at the border crossing, you can truthfully say that you don't know any password or passphrase to documents in your possession; only the assembly of 3 people can bring out the originals.
(3) Your company's long-term computer backups--made on network attached storage or to the cloud--are automatically encrypted. The decryption key can be shared between the system administrators and executives such that any 2 sysadmins or any 3 executives can recover the decryption key.